GAS EXCHANGE & PHYSIOLOGY Atmospheric Pressure Intra-Alveolar Pressure Inspiration 760 mm HG at Sea Level (= 1 atm) Pressure due to gases (N2, O2, CO2, Misc.) Pressure inside the alveolus (air sac) Phrenic nerve impulse causes diaphragm to contract(moves downward) Inspiratory intercostals muscles lift up and out Pulls the pleural sac outward Expands the alveolar sacs / alveolar pressure drops 3-6mm below atmospheric As air moves in the alveolar pressure goes towards atmospheric pressure Diaphragm/intercostals relaxes Expiration Puts pressure on the pleural sac Lungs naturally (elastically) recoil Expiration (w/ exertion) Bulk Flow Alveoli get smaller (increased alveolar p.) Normal movements, PLUS we use expiratory intercostals muscles Also abdominals and back muscles Movement of gas from an area of higher pressure to an area of lower pressure. Like Diffusion
Conduction Zone Warms & moistens, Cilia/mucous protects, Sound production, etc. Respiratory Zone mouth/nose pharynx larynx trachea bronchi bronchioles where gas exchange occurs respiratory bronchioles alveoli Remember, the lung is made up of lots of little air sacs and each small sac is surrounded by small capillaries. The inner surface of the alveoli is very moist. This causes surface tension and works against expanding the lungs. To counteract this surface tension certain alveolar cells (Type II Cells) secrete surfactant, which help increase compliance. Compliance is the degree & ease of expansion of the lung during inspiration. It depends on the trans-pulmonary pressure. In a healthy person a small change in pressure difference can cause great increases in volume of the lung spaces. Factors involved include: 1. Lung elasticity (Big problem when you have fibritic -type diseases) 2. Elastic forces due to surface tension of fluid in lung (Respiratory distress in newborns is due to malfunctioning type II cells) 3. Airway resistance: length of airway, radius of airway, neuro-endocrine and chemical factors. 4. Radius of airways depends on cartilage, lateral traction, smooth muscle, and pressure differences between outside and inside. 5. Carbon Dioxide Levels: Increased CO 2 causes dilation of airways (usually concurrent with a decrease in oxygen levels) 6. Nervous System Innervation: a. parasympathetic innervation causes constriction of airways(so does histamine allergic reaction) b. sympathetic innervation causes dilation of airways (epi reduces resistance and increases radius)
FLOW COMMON RESPIRATORY PROBLEMS ASTHMA Airways are constricted, Secretion of a thick mucous, Need to take bronchodilators ( albuterol ), & steroids ( pulmocort ) Trouble exhaling RESTRICTIVE LUNG DISEASE Problem with muscles, forced to take short shallow breaths CHRONIC OBSTRUCTIVE LUNG DISEASE (COPD) Chronic Bronchitis (excess fluid/mucous secretion) and Emphysema (breakdown of alveolar walls, decreased surface area, decreased gas exchange, pressure decreases as you exhale) Normal exhaling Damaged lung TIME
Partial Pressure: The total air pressure is the sum of the partial pressures of each gas in that solution/mixture. Sea-Level Atmospheric Partial Pressures ( Average Humidity ) Nitrogen: 78% of atmosphere = 593mm Oxygen: 21% of atmosphere = 152mm Carbon Dioxide: 0.04% of atm = 0.3mm *measure pco2 exhaled at the mouth & nose and it will be about 32mm before it diffuses away. Sea-Level Alveolar Partial Pressures ( Wet ) The air in the lung is wet and water vapor can take up to 47mm of the partial pressure. Oxygen: = 105mm Carbon Dioxide: = 40mm Color the numbers of the diagram. Red for p0 2 and Blue for pco 2 Question: Is Venous blood Deoxygenated or Lessoxygenated?
FACTORS AFFECTING TRANSPORT OF GAS IN LUNG AND TISSUE 1. Pressure Gradients 2. Surface Area Larger Gradient = More/ Faster Diffusion 3. Diffusion Distance Less Surface Area = Less Diffusion Larger Distance = Slower/ Less Diffusion
The oxygen has reached the alveolus and diffused down its gradient into the capillary now, how does this GAS enter the liquid? Gases are soluble in liquids! Remember chemistry class? Hemoglobin (HB) is specially designed to carry oxygen (and other gases like CO 2 and CO too) 100ml of plasma can dissolve 0.3ml oxygen 100ml of plasma with normal amounts of HB can hold 20ml of oxygen combined with HB + the 0.3 ml dissolved in solution. Each HB can hold 4 oxygen molecules Heme has an Iron group and globin refers to the protein which is made up of four polypeptide chains Cooperative Binding Hemoglobin has two states (Tense and Relaxed) It gets easier to add an O2 after another O2 is already there, and easier still with 3 rd & 4 th O2
Color the image of HB A) Iron B) Protein making up the second polypeptide subunit C) Heme Myoglobin This special oxygen-storing molecule found in skeletal muscle has only one subunit and no cooperative binding. It holds onto oxygen until the partial pressure of O2 is VERY low, then it dumps its store of Oxygen.
Hemoglobin Saturation The relative amount of oxygen in the blood compared to the carrying capacity of the hemoglobin is called the oxygen saturation, and is expressed as a percentage. It s directly proportional to the po2 the partial pressure of oxygen. The hemoglobin in arterial blood is only about 97% saturated with oxygen and the venous blood is about 75% saturated. Hemoglobin / Oxygen Dissociation Curve Because of cooperative binding, the O2/ HB dissociation curve looks like an S. At low po2 HB easily dumps its oxygen At high po2 HB likes to hang onto its oxygen Perfect! Dump O2 at the tissues and hold onto it at the lungs and in the blood!
po 2 Put your finger on a po 2 follow, it up to the chart and over to the left. po2 in exercising body tissues is VERy low, po2 in the lungs is about 105. HB is still 75% saturated with O2 after is passes through normal tissues.
The O2/HB curve can change in a few situations Increased CO2 Probably due to exercise Shifts the curve to the RIGHT Drops off O2 easier at higher po2 levels Increased H+ (Acidity) Increased DPG Shifts the curve to the RIGHT Drops off O2 easier at higher po2 levels Can be released from RBCs during times of Anemia (Not enough oxygen) High Altitude acclimatization Shifts the curve to the RIGHT Drops off O2 easier at higher po2 levels *Draw your finger from the po2 up to the curve and then over to the percent saturation for 40 and 105 for each of the three curves and make marks on the left axis as to where the percent saturation is for each curve. Fetal HB Has a curve that lies to the left of normal/mom Holds onto (steals) oxygen from mommy at all po2 levels
Transport of Oxygen 99% on HB Oxyhemoglobin 1% Dissolved in Plasma Transport of Carbon Dioxide 24% on HB Carboxyamino- Hemoglobin 9% Dissolved in Plasma 67% as Bicarbonate in the Plasma Bicarb Buffer System Buffer Review: CO2 + H2O H2CO3 H + + HCO3 -
Hypoxia Not enough Oxygen Getting to where it needs to go! Normal Color: A) CO2 B) Hemoglobin C) Blood D) Oxygen E) Lungs F) Cells Hypoxic Hypoxia Anemic Hypoxia Primary Oxygen Supply Deficient (Suffocation/ High Altitude / Blocked Airway / Inhibited Respiratory Center in Brain / Paralysis of Respiratory Muscles / Pneumonia) Stagnant Hypoxia Hemoglobin or RBC Deficiencey (Anemia) Histotoxic Hypoxia Blood is not flowing. (Ischemia / Shock / Bleeding) Normal Circulation, but Cells can t use the Oxygen (Poisoning with Cyanide!)
High Altitude Acclimatization Short Term Increased Ventilation (When skiing for a week) Increased Excretion of Bicarbonate Increased RBC Release of DPG Long Term (Move to Colorado) Increased RBC Production in Kidney (Stimulated by hormone Erythropoietin) Increased Capillary Growth Control of Ventilation by CO 2 Respiratory Center Ventral Surface of Medulla Oblongata Respiratory Center of the brain Cerebrospinal Fluid Increases in metabolism makes pco2 rise Increased pco2 makes the [H+] rise H+ diffuses into the CSF Brain (respiratory center) sends signals on Phrenic nerve to respiratory muscles to increase ventilation More CO2 is breathed out pco2 drops Control of Ventilation by O 2 Aortic & Carotid Bodies po2 drops Glossopharyngeal nerve (from carotid bodies) and Phrenic nerve (from aortic bodies) send signals to respiratory center Phrenic nerve to respiratory muscles to increase ventilation po2 rises *may require high altitude-type acclimatization also